Hi Ken,

Flea beetles do overwinter in soil as larvae. However, sterilizing the soil every spring is not the way to go. Whatever chemical measures applied the soil to kill flea beetles will also kill beneficial soil organisms. Thankfully, there are plenty of other flea beetle management practices. 

1. Trap Crops

• Flea beetles prefer crucifers. Using a crucifer as a sacrificial plant will attract flea beetles and consolidate them to a single plant that can be treated/ignored.

2. Reduce habitat

• Control weeds around plantings. Remove crop/plant debris.

3. General cultural controls

• Plant crops as late as possible. Encourage vigorous plant growth.

Chemical and biological controls against flea beetles are not very effective. That is because the beetles are very mobile, and can easily recolonize an area after treatment/extirpation. Here is the CSU fact sheet on flea beetles.

https://extension.colostate.edu/topic-areas/insects/flea-beetles-5-592/